Abstract: This paper explores the application of programmable controllers in intelligent maintenance, in response to the current low efficiency of secondary equipment maintenance in the power grid and the reliance on manual labor. A hierarchical intelligent maintenance system based on programmable controllers combines data collection, fault diagnosis, and automated operation to form a closed-loop process from monitoring the operating status to confirming and repairing. The case shows that the system can automatically handle faults and complete standard tests, improving typical maintenance efficiency by more than 70%, with standardized operation and traceable data. Practice has proven that PLC based maintenance system technology is feasible, significantly improving maintenance efficiency and quality, and providing effective solutions for automated state maintenance.